CHARLES S. HILL, C. E.Associate Editor, Engineering-Contracting

PREFACE.

(And CHAPTER I.)

How best to perform construction work and what it will cost
for
materials, labor, plant and general expenses are matters of vital
interest to engineers and contractors. This book is a treatise on the
methods and cost of concrete construction. No attempt has been made to
present the subject of cement testing which is already covered by Mr.
W.
Purves Taylor's excellent book, nor to discuss the physical properties
of cements and concrete, as they are discussed by Falk and by Sabin,
nor
to consider reinforced concrete design as do Turneaure and Maurer or
Buel and Hill, nor to present a general treatise on cements, mortars
and
concrete construction like that of Reid or of Taylor and Thompson. On
the contrary, the authors have handled the subject of concrete
construction solely from the viewpoint of the builder of concrete
structures. By doing this they have been able to crowd a great amount
of
detailed information on methods and costs of concrete construction into
a volume of moderate size.

Though the special information contained in the book is of
most
particular assistance to the contractor or engineer engaged in the
actual work of making and placing concrete, it is believed that it will
also prove highly useful to the designing engineer and to the
architect.
It seems plain that no designer of concrete structures can be a really
good designer without having a profound knowledge of methods of
construction and of detailed costs. This book, it is believed, gives
these methods and cost data in greater number and more thoroughly
analyzed than they can be found elsewhere in engineering literature.

The costs and other facts contained in the book have been
collected from
a multitude of sources, from the engineering journals, from the
transactions of the engineering societies, from Government Reports and
from the personal records of the authors and of other engineers and
contractors. It is but fair to say that the great bulk of the matter
contained in the book,[Pg iv]
though portions of it have appeared previously
in other forms in the authors' contributions to the technical press,
was
collected and worked up originally by the authors. Where this has not
been the case the original data have been added to and re-analyzed by
the authors. Under these circumstances it has been impracticable to
give
specific credit in the pages of the book to every source from which the
authors have drawn aid. They wish here to acknowledge, therefore, the
help secured from many engineers and contractors, from the volumes of
Engineering News, Engineering Record and Engineering-Contracting, and
from the Transactions of the American Society of Civil Engineers and
the
proceedings and papers of various other civil engineering societies and
organizations of concrete workers. The work done by these journals and
societies in gathering and publishing information on concrete
construction is of great and enduring value and deserves full
acknowledgment.

In answer to any possible inquiry as to the relative parts of
the work
done by the two authors in preparing this book, they will answer that
it
has been truly the labor of both in every part.

TABLE OF CONTENTS.

PAGE

CHAPTER I.—METHODS AND COST OF SELECTING AND PREPARING
MATERIALS FOR CONCRETE. 1

Cement: Portland Cement—Natural
Cement—Slag Cement—Size and Weight of
Barrels of Cement—Specifications and Testing. Sand:
Properties of Good
Sand—Cost of Sand—Washing Sand; Washing with Hose;
Washing with Sand
Ejectors; Washing with Tank Washers. Aggregates:
Broken
Stone—Gravel—Slag and Cinders—Balanced
Aggregate—Size of
Aggregate—Cost of Aggregate—Screened and Crusher
Run Stone for
Concrete—Quarrying and Crushing Stone—Screening and
Washing Gravel.

CHAPTER II.—THEORY AND PRACTICE OF PROPORTIONING CONCRETE. 25

Voids: Voids in Sand; Effect of
Mixture—Effect of Size of Grains—Voids
in Broken Stone and Gravel; Effect of Method of Loading; Test
Determinations; Specific Gravity; Effect of Hauling—Theory of
the
Quantity of Cement in Mortar; Tables of Quantities in
Mortar—Tables of
Quantities in Concrete—Percentage of Water in
Concrete—Methods of
Measuring and Weighing; Automatic Measuring Devices.

CHAPTER III.—METHODS AND COSTS OF MAKING AND PLACING
CONCRETE BY HAND. 45

Loading into Stock Piles—Loading from Stock
Piles—Transporting
Materials to Mixing Boards—Mixing—Loading and
Hauling Mixed
Concrete—Dumping, Spreading and Ramming—Cost of
Superintendence—Summary of Costs.

CHAPTER IV.—METHODS AND COST OF MAKING AND PLACING
CONCRETE BY MACHINE. 61

Imperfectly Made Forms—Imperfect Mixing and
Placing—Efflorescence—Spaded and Troweled
Finishes—Plaster and Stucco
Finish—Mortar and Cement Facing—Special Facing
Mixtures for Minimizing
Form Marks—Washes—Finishing by Scrubbing and
Washing—Finishing by
Etching with Acid—Tooling Concrete Surfaces—Gravel
or Pebble Surface
Finish—Colored Facing.

CHAPTER IX.—METHODS AND COST OF FORM CONSTRUCTION 136

Introduction—Effect of Design on Form Work—Kind of
Lumber—Finish and
Dimensions of Lumber—Computation of Forms—Design
and
Construction—Unit Construction of Forms—Lubrication
of
Forms—Falsework and Bracing—Time for and Method of
Removing
Forms—Estimating and Cost of Form Work.

Introduction—Molding Piles in Place; Method of Constructing
Raymond
Piles; Method of Constructing Simplex Piles; Method of Constructing
Piles with Enlarged Footings; Method of Constructing Piles
by the Compressol System; Method of Constructing Piers in
Caissons—Molding
Piles for Driving—Driving Molded Piles: Method and Cost
of Molding and Jetting Piles for an Ocean Pier; Method of Molding
and Jetting Square Piles for a Building Foundation; Method of Molding
and Jetting Corrugated Piles for a Building Foundation; Method of
Molding and Driving Round Piles; Molding and Driving Square Piles
for a Building Foundation; Method of Molding and Driving Octagonal
Piles—Method and Cost of Making Reinforced Piles by Rolling.

CHAPTER XI.—METHODS AND COST OF HEAVY CONCRETE WORK
IN FORTIFICATIONS, LOCKS, DAMS, BREAKWATERS AND
PIERS 184

CHAPTER XV.—METHODS AND COST OF CONSTRUCTING SIDEWALKS,
PAVEMENTS, AND CURB AND GUTTER 307

Introduction—Cement Sidewalks: General
Method of Construction—Bonding
of Wearing Surface and Base—Protection of Work from Sun and
Frost—Cause and Prevention of Cracks—Cost of Cement
Walks; Toronto,
Ont.; Quincy, Mass.; San Francisco, Cal.; Cost in Iowa. Concrete
Pavement: Windsor, Ontario—Richmond, Ind. Concrete
Curb and Gutter:
Form Construction—Concrete Mixtures and
Concreting—Cost of Curb and
Gutter: Ottawa, Canada; Champaign, Ill.

Introduction—Drilling and Blasting Concrete—Bench
Monuments, Chicago,
III.—Pole Base—Mile Post—Bonding New
Concrete to Old—Dimensions and
Capacities of Mixers—Data for Estimating Weight of Steel in
Reinforced
Concrete; Computing Weight from Percentage of Volume; Weights and
Dimensions of Plain and Special Reinforcing Metals—Recipes
for Coloring
Mortars.

Concrete Construction Methods and Cost

CHAPTER I.

METHODS AND COST OF SELECTING AND PREPARING MATERIALS FOR
CONCRETE.

Concrete is an artificial stone produced by mixing cement
mortar with
broken stone, gravel, broken slag, cinders or other similar fragmentary
materials. The component parts are therefore hydraulic cement, sand and
the broken stone or other coarse material commonly designated as the
aggregate.

CEMENT.

At least a score of varieties of hydraulic cement are listed
in the
classifications of cement technologists. The constructing engineer and
contractor recognize only three varieties: Portland cement, natural
cement and slag or puzzolan cement. All concrete used in engineering
work is made of either Portland, natural or slag cement, and the great
bulk of all concrete is made of Portland cement. Only these three
varieties of cement are, therefore, considered here and they only in
their aspects having relation to the economics of construction work.
For
a full discussion of the chemical and physical properties of hydraulic
cements and for the methods of determining these properties by tests,
the reader is referred to "Practical Cement Testing," by W. Purves
Taylor.

PORTLAND CEMENT.—Portland cement
is the best of the hydraulic cements.
Being made from a rigidly controlled artificial mixture of lime, silica
and alumina the product of the best mills is a remarkably strong,
uniform and stable material. It is suitable for all classes of concrete
work and is the only variety of hydraulic cement allowable for
reinforced concrete or for plain concrete having to endure hard[Pg
2] wear or
to be used where strength, density and durability of high degree are
demanded.

NATURAL CEMENT.—Natural cement
differs from Portland cement in degree
only. It is made by calcining and grinding a limestone rock containing
naturally enough clayey matter (silica and alumina) to make a cement
that will harden under water. Owing to the imperfection and
irregularity
of the natural rock mixture, natural cement is weaker and less uniform
than Portland cement. Natural cement concrete is suitable for work in
which great unit strength or uniformity of quality is not essential. It
is never used for reinforced work.

SLAG CEMENT.—Slag cement has a
strength approaching very closely that
of Portland cement, but as it will not stand exposure to the air slag
cement concrete is suitable for use only under water. Slag cement is
made by grinding together slaked lime and granulated blast furnace slag.

SIZE AND WEIGHT OF BARRELS OF CEMENT.—The
commercial unit of
measurement of cement is the barrel; the unit of shipment is the bag. A
barrel of Portland cement contains 380 lbs. of cement, and the barrel
itself weighs 20 lbs.; there are four bags (cloth or paper sacks) of
cement to the barrel, and the regulation cloth sack weighs
1½ lbs.
The size of cement barrels varies, due to the differences in weight of
cement and to differences in compacting the cement into the barrel. A
light burned Portland cement weighs 100 lbs. per struck bushel; a heavy
burned Portland cement weighs 118 to 125 lbs. per struck bushel. The
number of cubic feet of packed Portland cement in a barrel ranges from
3
to 3½. Natural cements are lighter than Portland cement. A
barrel of
Louisville, Akron, Utica or other Western natural cement contains 265
lbs. of cement and weighs 15 lbs. itself; a barrel of Rosendale or
other
Eastern cement contains 300 lbs. of cement and the barrel itself weighs
20 lbs. There are 3¾ cu. ft. in a barrel of Louisville
cement. Usually
there are three bags to a barrel of natural cement.

As stated above, the usual shipping unit for cement is the
bag, but
cement is often bought in barrels or, for large works, in bulk. When
bought in cloth bags, a charge is made of[Pg 3]
10 cts. each for the bags,
but on return of the bags a credit of 8 to 10 cts. each is allowed.
Cement bought in barrels costs 10 cts. more per barrel than in bulk,
and
cement ordered in paper bags costs 5 cts. more per barrel than in bulk.
Cement is usually bought in cloth sacks which are returned, but to get
the advantage of this method of purchase the user must have an accurate
system for preserving, checking up and shipping the bags.

Where any considerable amount of cement is to be used the
contractor
will find that it will pay to erect a small bag house or to close off a
room at the mixing plant. Provide the enclosure with a locked door and
with a small window into which the bags are required to be thrown as
fast as emptied. One trustworthy man is given the key and the task of
counting up the empty bags each day to see that they check with the
bags
of cement used. The following rule for packing and shipping is given by
Gilbreth.[A]

"Pack cement bags laid flat, one on top of the other, in piles
of 50.
They can then be counted easily. Freight must be prepaid when cement
bags are returned and bills of lading must be obtained in duplicate or
credit cannot be obtained on shipment."

The volumes given above are for cement compacted in the
barrel. When the
cement is emptied and shoveled into boxes it measures from 20 to 30 per
cent more than when packed in the barrel. The following table compiled
from tests made for the Boston Transit Commission, Mr. Howard Carson,
Chief Engineer, in 1896, shows the variation in volume of cement
measured loose and packed in barrels:

Brand

Vol. Barrel cu. ft.

Vol. Packed cu. ft.

Vol. Loose cu. ft.

Per cent Increase in bulk

Portland.

Giant

3.5

3.35

4.17

25

Atlas

3.45

3.21

3.75

18

Saylors

3.25

3.15

4.05

30

Alsen

3.22

3.16

4.19

33

Dyckerhoff

3.12

3.03

4.00

33

Mr. Clarence M. Foster is authority for the statement that[Pg
4] Utica cement
barrels measure 16¼ ins. across at the heads, 19½
ins. across the
bilge, and 25¾ ins. in length under heads, and contain 3.77
cu. ft.
When 265 lbs. of Utica natural hydraulic cement are packed in a barrel
it fills it within 2½ ins. of the top and occupies 3.45 cu.
ft., and
this is therefore the volume of a barrel of Utica hydraulic cement
packed tight.

In comparative tests made of the weights and volumes of
various brands
of cements at Chicago in 1903, the following figures were secured:

Vol. per bbl., cu. ft.

Weight per bbl., lbs.

Weight per cu. ft.

Brand.

Loose.

Gross.

Net.

Loose, lbs.

Dyckerhoff

4.47

395

369.5

83

Atlas

4.45

401

381

85.5

Alpha

4.37

400.5

381

86.5

Puzzolan

4.84

375

353.5

73.5

Steel

4.96

345

322.5

67.5

Hilton

4.64

393

370.5

79.5

SPECIFICATIONS AND TESTING—The
great bulk of cement used in
construction work is bought on specification. The various government
bureaus, state and city works departments, railway companies, and most
public service corporations have their own specifications. Standard
specifications are also put forward by several of the national
engineering societies, and one of these or the personal specification
of
the engineer is used for individual works. Buying cement to
specification necessitates testing to determine that the material
purchased meets the specified requirements. For a complete discussion
of
the methods of conducting such tests the reader is referred to
"Practical Cement Testing" by W. Purves Taylor.

According to this authority a field testing laboratory will
cost for
equipment $250 to $350. Such a laboratory can be operated by two or
three men at a salary charge of from $100 to $200 per month. Two men
will test on an average four samples per day and each additional man
will test four more samples. The cost of testing will range from $3 to
$5 per sample, which is roughly equivalent to 3 cts. per barrel of[Pg
5]
cement, or from 3 to 5 cts. per cubic yard of concrete. These figures
are for field laboratory work reasonably well conducted under
ordinarily
favorable conditions. In large laboratories the cost per sample will
run
somewhat lower.

SAND.

Sand constitutes from ⅓ to ½ of the
volume of concrete; when a large
amount of concrete is to be made a contractor cannot, therefore, afford
to guess at his source of sand supply. A long haul over poor roads can
easily make the sand cost more than the stone per cubic yard of
concrete.

PROPERTIES OF GOOD SAND.—Engineers
commonly specify that sand for
concrete shall be clean and sharp, and silicious in character. Neither
sharpness nor excessive cleanliness is worth seeking after if it
involves much expense. Tests show conclusively that sand with rounded
grains makes quite as strong a mortar, other things being equal, as
does
sand with angular grains. The admixture with sand of a considerable
percentage of loam or clay is also not the unmixed evil it has been
supposed to be. Myron S. Falk records[B] a number of elaborate
experiments on this point. These experiments demonstrate conclusively
that loam and clay in sand to the amount of 10 to 15 per cent. result
in
no material reduction in the strength of mortars made with this sand as
compared with mortars made with the same sand after washing. There can
be no doubt but that for much concrete work the expense entailed in
washing sand is an unnecessary one.

The only substitute for natural sand for concrete, that need
be
considered practically, is pulverized stone, either the dust and fine
screenings produced in crushing rock or an artificial sand made by
reducing suitable rocks to powder. As a conclusion from the records of
numerous tests, M. S. Falk says: "It may be concluded that rock
screenings may be substituted for sand, either in mortar or concrete,
without any loss of strength resulting. This is important commercially,
for it precludes the necessity of screening the dust from crushed rock
and avoids, at the same time, the cost of procuring a natural sand to
take its place."[Pg 6]

The principal danger in using stone dust is failure to secure
the proper
balance of different size grains. This is also an important matter in
the choice of natural sands. Sand composed of a mixture of grains
ranging from fine to coarse gives uniformly stronger mortars than does
sand with grains of nearly one size, and as between a coarse and a fine
sand of one size of grains the coarse sand gives the stronger mortar.
Further data on the effect of size of grains on the utility of sand for
concrete are given in Chapter II, in the section on Voids in Sand, and
for those who wish to study in detail, the test data on this and the
other matters referred to here, the authors recommend "Cements, Mortars
and Concretes; Their Physical Properties," by Myron S. Falk.

COST OF SAND.—A very common price
for sand in cities is $1 per cu. yd.,
delivered at the work. It may be noted here that as sand is often sold
by the load instead of the cubic yard, it is wise to have a written
agreement defining the size of a load. Where the contractor gets his
sand from the pit its cost will be the cost of excavating and loading
at
the pit, the cost of hauling in wagons, the cost of freight and
rehandling it if necessary, and the cost of washing, added together.

An energetic man working under a good foreman will load 20 cu.
yds. of
sand into wagons per 10-hour day; with a poor foreman or when laborers
are scarce, it is not safe to count on more than 15 cu. yds. per day.
With wages at $1.50 per day this will make the cost of loading 10 cts.
per cubic yard. The cost of hauling will include the cost of lost team
time and dumping, which will average about 5 cts. per cubic yard. With
1
cu. yd. loads, wages of team 35 cts. per hour, and speed of travel
2½
miles per hour, the cost of hauling proper is ½ ct. per 100
ft., or 27
cts. per mile. Assuming a mile haul, the cost of sand delivered based
on
the above figures will be 10 cts. + 5 cts. + ½ ct. per 100
ft. = 15 +
27 cts. = 42 cts. per cu. yd. Freight rates can always be secured and
it
is usually safe to estimate the weight on a basis of 2,700 lbs. per
cubic yard. For a full discussion of the cost of excavating sand and
other earths the reader is referred to "Earth Excavation and
Embankments; Methods and Cost," by Halbert P. Gillette and Daniel J.
Hauer.[Pg 7]

METHODS AND COST OF WASHING SAND.—When
the available sand carries
considerable percentages of loam or clay and the specifications require
that clean sand shall be used, washing is necessary. The best and
cheapest method of performing this task will depend upon the local
conditions and the amount of sand to be washed.

Washing With Hose.—When the
quantity of sand to be washed does not
exceed 15 to 30 cu. yds. per day the simplest method, perhaps, is to
use
a hose. Build a wooden tank or box, 8 ft. wide and 15 ft. long, the
bottom having a slope of 8 ins. in the 15 ft. The sides should be about
8 ins. high at the lower end and rise gradually to 3 ft. in height at
the upper end. Close the lower end of the tank with a board gate about
6
ins. in height and sliding in grooves so that it can be removed. Dump
about 3 cu. yds. of sand into the upper end of the tank and play a
¾-in. hose stream of water on it, the hose man standing at
the lower
end of the tank. The water and sand flow down the inclined bottom of
the
tank where the sand remains and the dirt flows over the gate and off
with the water. It takes about an hour to wash a 3-cu. yd. batch, and
by
building a pair of tanks so that the hose man can shift from one to the
other, washing can proceed continuously and one man will wash 30 cu.
yds. per 10-hour day at a cost, with wages at $1.50, of 5 cts. per
cubic
yard. The sand, of course, has to be shoveled from the tank and this
will cost about 10 cts. per cubic yard, making 15 cts. per cubic yard
for washing and shoveling, and to this must be added any extra hauling
and, if the water is pumped, the cost of pumping which may amount to 10
cts. per cubic yard for coal and wages. Altogether a cost of from 15 to
30 cts. per cubic yard may be figured for washing sand with a hose.

Fig. 1.—Plan and Elevation of
Two-Hopper Ejector Sand
Washing Plant.

Fig. 2.—Plan and Elevation of
Four-Hopper Ejector Sand
Washing-Plant.

Washing With Sand Ejectors.—When
large quantities of sand are to be
washed use may be made of the sand ejector system, commonly employed in
washing filter sand at large water filtration plants; water under
pressure is required. In this system the dirty sand is delivered into a
conical or pyramidal hopper, from the bottom of which it is drawn by an
ejector and delivered mixed with water into a second similar hopper;
here the water and dirt overflow the top of the hopper,[Pg
8] while the sand
settles and is again ejected into a third hopper or to the stock pile
or
bins. The system may consist of anywhere from two to six hoppers.
Figure
1 shows a two-hopper lay-out and Fig. 2 shows a four-hopper lay-out. In[Pg
9]
the first plant the washed sand is delivered into bins so arranged, as
will be seen, that the bins are virtually a third washing hopper. The
clean sand is chuted from these bins directly into cars or wagons. In
the second plant the clean sand is ejected into a trough which leads it
into buckets handled by a derrick. The details of one of the washing
hoppers for the plant shown by Fig. 1 are illustrated by Fig. 3.

Fig. 3.—Details of Washing Hopper
and Ejector for Plant
Shown by Fig. 1.

At filter plants the dirty sand is delivered mixed with water
to the
first hopper by means of ejectors stationed in the filters and
discharging through pipes to the washers. When, as would usually be the
case in contract work, the sand is delivered comparatively dry to the
first hopper, this hopper must be provided with a sprinkler pipe to wet
the sand. In studying the ejector washing plants illustrated it should
be borne in mind that for concrete work they would not need to be of
such permanent construction as for filter plants, the washers would be
mounted on timber frames, underground piping would be done away with,
etc.; at best, however, such plants are expensive and will be warranted
only when the amount of sand to be washed is large.

The usual assumption of water-works engineers is that the
volume of
water required for washing filter sand is 15 times the volume of the
sand washed. At the Albany, N. Y., filters the sand passes through five
ejectors at the rate of 3 to 5 cu.[Pg 10]
yds. per hour and takes 4,000
gallons of water per cubic yard. One man shovels sand into the washer
and two take it away. Based on an output of 32 cu. yds. in 10 hours,
Mr.
Allen Hazen estimates the cost of washing as follows:

3 men, at $2 per day

$6.00

110,000 gallons of water, at $0.05

5.50

———

Total, 32 cu. yds., at 36 cts.

$11.50

Washing With Tank Washers.—Figure
4 shows a sand washer used in
constructing a concrete lock at Springdale, Pa., in the United States
government improvement work on the Allegheny river. The device
consisted
of a circular tank 9 ft. in diameter and 7 ft. high, provided with a
sloping false bottom perforated with 1-in. holes, through which water
was forced as indicated. A 7½×5×6-in.
pump with a 3-in. discharge pipe
was used to force water into the tank, and the rotating paddles were
operated by a 7 h.p. engine. This apparatus washed a batch of 14 cu.
yds. in from 1 to 2 hours at a cost of 7 cts. per cubic yard. The sand
contained much fine coal and silt. The above data are given by Mr. W.
H.
Roper.

Fig. 4.—Details of Tank Washer
Used at Springdale, Pa.

Fig. 5.—Details of Tank Washer
Used at Yonkers, N. Y.

Fig. 6.—Details of Rotating Tank
Sand Washer Used at
Hudson, N. Y.

Another form of tank washer, designed by Mr. Allen Hazen, for
washing
bank sand at Yonkers, N. Y., is shown by Fig. 5. This apparatus
consisted of a 10×2½×2½ ft.
wooden box, with a 6-in. pipe entering one
end at the bottom and there[Pg 11]
branching into three 3-in. pipes, extending
along the bottom and capped at the ends. The undersides of the 3-in.
pipes were pierced with ½-in. holes 6 ins. apart, through
which water
under pressure was discharged into the box. Sand was shoveled into the
box at one end and the upward currents of water raised the fine and
dirty particles until they escaped through the waste troughs. When the
box became filled with sand a sliding door at one end was opened and
the
batch discharged. The operation was continuous as long as sand was
shoveled into the box; by manipulating the door the sand could be made
to run out with a very small percentage of[Pg 12]
water. Sand containing 7 per
cent of dirt was thus washed so that it contained only 0.6 per cent
dirt. The washer handled 200 cu. yds. of sand in 10 hours. The above
data are given by F. H. Stephenson.

A somewhat more elaborate form of tank washer than either of
those
described is shown by Fig. 6. This apparatus was used by Mr. Geo. A.
Soper for washing filter sand at Hudson, N. Y. The dirty sand was
shoveled into a sort of hopper, from which it was fed by a hose stream
into an inclined cylinder, along which it traveled and was discharged
into a wooden trough provided with a screw conveyor and closed at both
ends. The water overflowing the sides of the trough carried away the
dirt and the clean sand was delivered by the screw to the bucket
elevator which hoisted it to a platform, from which it was taken by
barrows to the stock pile. A 4-h.p. engine with a 5-h.p. boiler
operated
the cylinder, screw, elevator and pump. Four men operated the washer
and
handled 32 cu. yds. of sand per day; with wages at $1.50 the cost of
washing was 20 cts. per cubic yard.

Fig. 7.—Arrangement of Sand
Washing Plant at Lynchburg,
Va.

In constructing a concrete block dam at Lynchburg, Va., sand
containing
from 15 to 30 per cent. of loam, clay and[Pg 13]
vegetable matter was washed
to a cleanliness of 2 to 5 per cent of such matter by the device shown
by Fig. 7. A small creek was diverted, as shown, into a wooden flume
terminating in two sand tanks; by means of the swinging gate the flow
was passed through either tank as desired. The sand was hauled by wagon
and shoveled into the upper end of the flume; the current carried it
down into one of the tanks washing the dirt loose and carrying it off
with the overflow over the end of the tank while the sand settled in
the
tank. When one tank was full the flow was diverted into the other tank
and the sand in the first tank was shoveled out, loaded into wagons,
and
hauled to the stock pile. As built this washer handled about 30 cu.
yds.
of sand per 10-hour day, but the tanks were built too small for the
flume, which could readily handle 75 cu. yds. per day with no larger
working force. This force consisted of three men at $1.50 per day,
making the cost, for a 30 cu. yd. output, 15 cts. per cu. yd. for
washing.

None of the figures given above includes the cost of handling
the sand
to and from the washer. When this involves much extra loading and
hauling, it amounts to a considerable expense, and in any plan for
washing sand the contractor should figure, with exceeding care, the
extra handling due to the necessity of washing.

AGGREGATES.

The aggregates commonly used in making concrete are broken or
crushed
stone, gravel, slag and cinders. Slag and cinders make a concrete that
weighs considerably less than stone or gravel mixtures, and being the
products of combustion are commonly supposed to make a specially fire
resisting concrete; their use is, therefore, confined very closely to
fireproof building work and, in fact, to floor construction for such
buildings. Slag and cinder concretes are for this reason given minor
consideration in this volume.

BROKEN STONE.—Stone produced by
crushing any of the harder and tougher
varieties of rock is suitable for concrete. Perhaps the best stone is
produced by crushing trap rock. Crushed trap besides being hard and
tough is angular and has an excellent fracture surface for holding
cement; it also withstands heat better than most stone. Next to[Pg
14] trap
the hard, tough, crystalline limestones make perhaps the best all
around
concrete material; cement adheres to limestone better than to any other
rock. Limestone, however, calcines when subjected to fire and is,
therefore, objected to by many engineers for building construction. The
harder and denser sandstones, mica-schists, granites and syanites make
good stone for concrete and occasionally shale and slate may be used.

GRAVEL.—Gravel makes one of the
best possible aggregates for concrete.
The conditions under which gravel is produced by nature make it
reasonably certain that only the tougher and harder rocks enter into
its
composition; the rounded shapes of the component particles permit
gravel
to be more closely tamped than broken stone and give less danger of
voids from bridging; the mixture is also generally a fairly well
balanced composition of fine and coarse particles. The surfaces of the
particles being generally smooth give perhaps a poorer bond with the
cement than most broken stone. In the matter of strength the most
recent
tests show that there is very little choice between gravel and broken
stone concrete.

SLAG AND CINDERS.—The slag used
for concrete aggregate is iron blast
furnace slag crushed to proper size. Cinders for aggregate are steam
boiler cinders; they are best with the fine ashes screened out and
should not contain more than 15 per cent. of unburned coal.

BALANCED AGGREGATE.—With the
aggregate, as with the sand for concrete,
the best results, other things being equal, will be secured by using a
well-balanced mixture of coarse and fine particles. Usually the product
of a rock crusher is fairly well balanced except for the very fine
material. There is nearly always a deficiency of this, which, as
explained in a succeeding section, has to be supplied by adding sand.
Usually, also, the engineer accepts the crusher product coarser than
screenings as being well enough balanced for concrete work, but this is
not always the case. Engineers occasionally demand an artificial
mixture
of varying proportions of different size stones and may even go so far
as to require gravel to be screened and reproportioned. This[Pg
15] artificial
grading of the aggregate adds to the cost of the concrete in some
proportion which must be determined for each individual case.

SIZE OF AGGREGATE.—The size of
aggregate to be used depends upon the
massiveness of the structure, its purpose, and whether or not it is
reinforced. It is seldom that aggregate larger than will pass a 3-in.
ring is used and this only in very massive work. The more usual size is
2½ ins. For reinforced concrete 1¼ ins. is about
the maximum size
allowed and in building work 1-in. aggregate is most commonly used.
Same
constructors use no aggregate larger than ¾ in. in
reinforced building
work, and others require that for that portion of the concrete coming
directly in contact with the reinforcement the aggregate shall not
exceed ¼ to ½ in. The great bulk of concrete work
is done with aggregate
smaller than 2 ins., and as a general thing where the massiveness of
the
structure will allow of much larger sizes it will be more economic to
use rubble concrete. (See Chapter VI.)

COST OF AGGREGATE.—The locality
in which the work is done determines
the cost of the aggregate. Concerns producing broken stone or screened
and washed gravel for concrete are to be found within shipping distance
in most sections of the country so that these materials may be
purchased
in any amount desired. The cost will then be the market price of the
material f. o. b. cars at plant plus the freight rates and the cost of
unloading and haulage to the stock piles. If the contractor uses a
local
stone or gravel the aggregate cost will be, for stone the costs of
quarrying and crushing and transportation, and, for gravel, the cost of
excavation, screening, washing and transportation.

SCREENED OR CRUSHER-RUN STONE FOR CONCRETE.—Formerly
engineers almost
universally demanded that broken stone for concrete should have all the
finer particles screened out. This practice has been modified to some
considerable extent in recent years by using all the crusher product
both coarse and fine, or, as it is commonly expressed, by using
run-of-crusher stone. The comparative merits of screened and
crusher-run
stone for concrete work are questions[Pg 16]
of comparative economy and
convenience. The fine stone dust and chips produced in crushing stone
are not, as was once thought, deleterious; they simply take the place
of
so much of the sand which would, were the stone screened, be required
to
balance the sand and stone mixture. It is seldom that the proportion of
chips and dust produced in crushing stone is large enough to replace
the
sand constituent entirely; some sand has nearly always to be added to
run-of-crusher stone and it is in determining the amount of this
addition that uncertainty lies. The proportions of dust and chips in
crushed stone vary with the kind of stone and with the kind of crusher
used. Furthermore, when run-of-crusher stone is chuted from the crusher
into a bin or pile the screenings and the coarse stones segregate.
Examination of a crusher-run stone pile will show a cone-shaped heart
of
fine material enclosed by a shell of coarser stone, consequently when
this pile of stone is taken from to make concrete a uniform mixture of
fine and coarse particles is not secured, the material taken from the
outside of the pile will be mostly coarse and that from the inside
mostly fine. This segregation combined with the natural variation in
the
crusher product makes the task of adding sand and producing a balanced
sand and stone mixture one of extreme uncertainty and some difficulty
unless considerable expenditure is made in testing and reproportioning.
When the product of the crusher is screened the task of proportioning
the sand to the stone is a straightforward operation, and the screened
out chips and dust can be used as a portion of the sand if desired. The
only saving, then, in using crusher-run stone direct is the very small
one of not having to screen out the fine material. The conclusion must
be that the economy of unscreened stone for concrete is a very doubtful
quantity, and that the risk of irregularity in unscreened stone
mixtures
is a serious one. The engineer's specifications will generally
determine
for the contractor whether he is to use screened or crusher-run stone,
but these same specifications will not guarantee the regularity of the
resulting concrete mixture; this will be the contractor's burden and if
the engineer's inspection is rigid and the crusher-run product runs
uneven for the reasons given above it will[Pg 17]
be a burden of considerable
expense. The contractor will do well to know his product or to know his
man before bidding less or even as little on crusher-run as on screened
stone concrete.

COST OF QUARRYING AND CRUSHING STONE.—The
following examples of the
cost of quarrying and crushing stone are fairly representative of the
conditions which would prevail on ordinary contract work. In quarrying
and crushing New Jersey trap rock with gyratory crushers the following
was the cost of producing 200 cu. yds. per day:

Per day.

Per cu. yd.

3 drillers at $2.75

$ 8.25

$0.041

3 helpers at $1.75

5.25

0.026

10 men barring out and sledging

15.00

0.075

14 men loading carts

21.00

0.105

4 cart horses

6.00

0.030

2 cart drivers

3.00

0.015

2 men dumping carts and feeding
crusher

3.00

0.015

1 fireman for drill boiler

2.50

0.013

1 engineman for crusher

3.00

0.015

1 blacksmith

3.00

0.015

1 blacksmith helper

2.00

0.010

1 foreman

5.00

0.025

2 tons coal at $3.50

7.00

0.035

150 lbs. 40% dynamite at 15 cts.

22.50

0.113

———

———

Total

$106.50

$0.533

The quarry face worked was 12 to 18 ft., and the stone was
crushed to
2-in. size. Owing to the seamy character of the rock it was broken by
blasting into comparatively small pieces requiring very little
sledging.
The stone was loaded into one-horse dump carts, the driver taking one
cart to the crusher while the other was being loaded. The haul was 100
ft. The carts were dumped into an inclined chute leading to a No. 5
Gates crusher. The stone was elevated by a bucket elevator and
screened.
All stone larger than 2 ins. was returned through a chute to a No. 3
Gates crusher for[Pg 18] recrushing. The
cost given above does not include
interest, depreciation, and repairs; these items would add about $8 to
$10 more per day or 4 to 5 cts. per cubic yard.

In quarrying limestone, where the face of the quarry was only
5 to 6 ft.
high, and where the amount of stripping was small, one steam drill was
used. This drill received its steam from the same boiler that supplied
the crusher engine. The drill averaged 60 ft. of hole drilled per
10-hr.
day, but was poorly handled and frequently laid off for repairs. The
cost of quarrying and crushing was as follows:

Quarry.

1 driller

$ 2.50

1 helper

1.50

1 man stripping

1.50

4 men quarrying

6.00

1 blacksmith

2.50

⅛ ton coal at $3

1.00

Repairs to drill

.60

Hose, drill steel and interest on
plant

.90

24 lbs. dynamite

3.60

———

Total

$20.10

Crusher.

1 engineman

$ 2.50

2 men feeding crusher

3.50

6 men wheeling

9.00

1 bin man

1.50

1 general foreman

3.00

⅓ ton coal at $3

1.00

1 gallon oil

.25

Repairs to crusher

1.00

Repairs to engine and boiler

1.00

Interest on plant

1.00

———

Total

$23.75

Summary:

Per day.

Per. cu. yd.

Quarrying

$20.10

$0.37

Crushing

23.75

0.39

———

——

Total for 60 cu. yds.

$43.85

$0.76

The "4 men quarrying" barred out and sledged the stone to
sizes that
would enter a 9×16-in. jaw crusher. The "6 men wheeling"
delivered the
stone in wheelbarrows to the crusher platform, the run plank being
never
longer than 150 ft. Two men fed the stone into the crusher, and a
bin-man helped load the wagons from the bin, and kept tally of the
loads. The stone was measured loose in the wagons, and it was found
that
the average load was 1½ cu. yds., weighing 2,400 lbs. per
cu. yd. There
were 40 wagon loads, or 60 cu. yds.[Pg 19]
crushed per 10-hr. day, although on
some days as high as 75 cu. yds. were crushed. The stone was screened
through a rotary screen, 9 ft. long, having three sizes of openings,
½-in., 1¼-in. and 2¼-in. The output
was 16% of the smallest size, 24% of
the middle size, and 60% of the large size. All tailings over
2½ ins. in
size were recrushed.

It will be noticed that the interest on the plant is quite an
important
item. This is due to the fact that, year in and year out, a quarrying
and crushing plant seldom averages more than 100 days actually worked
per year, and the total charge for interest must be distributed over
these 100 days, and not over 300 days as is so commonly and erroneously
done. The cost of stripping the earth off the rock is often
considerably
in excess of the above given cost, and each case must be estimated
separately. Quarry rental or royalty is usually not in excess of 5 cts.
per cu. yd., and frequently much less. The dynamite used was 40%, and
the cost of electric exploders is included in the cost given. Where a
higher quarry face is used the cost of drilling and the cost of
explosives per cu. yd. is less. Exclusive of quarry rent and heavy
stripping costs, a contractor should be able to quarry and crush
limestone or sandstone for not more than 75 cts. per cu. yd., or 62
cts.
per ton of 2,000 lbs., wages and conditions being as above given.

The labor cost of erecting bins and installing a
9×16 jaw crusher,
elevator, etc., averages about $75, including hauling the plant two or
three miles, and dismantling the plant when work is finished.

The following is a record of the cost of crushing stone and
cobbles on
four jobs at Newton, Mass., in 1891. On jobs A and B the stone was
quarried and crushed; on jobs C and D cobblestones were crushed. A
9×15-in. Farrel-Marsondon crusher was used, stone being fed
in by two
laborers. A rotary screen having ½, 1 and 2½-in.
openings delivered the
stone into bins having four compartments, the last receiving the
"tailings" which had failed to pass through the screen. The broken
stone
was measured in carts as they left the bin, but several cart loads were
weighed, giving the following weights per cubic foot of broken stone:[Pg
20]

Note.—"A" was trap rock; "B" was conglomerate rock;
"C" and
"D" were trap and granite cobblestones. Common laborers on jobs
"A" and "D" were paid $1.75 per 9-hr. day; on jobs "B" and "C,"
$1.50 per 9-hr. day; two-horse cart and driver, $5 per day;
blacksmith, $2.50; engineer on crusher, $2 on job "A," $2.25 on
"B," $2.00 on "C," $2.50 on "D"; steam driller received $3, and
helper $1.75 a day; foreman, $3 a day. Coal was $5.25 per short
ton. Forcite powder, 11⅓ cts. per lb.

For a full discussion of quarrying and crushing methods and
costs and
for descriptions of crushing machinery and plants the reader is
referred
to "Rock Excavation; Methods and Cost," by Halbert P. Gillette.

SCREENING AND WASHING GRAVEL.—Handwork
is resorted to in screening
gravel only when the amount to be screened is small and when it is
simply required to separate the fine sand without sorting the coarser
material into sizes. The gravel is shoveled against a portable inclined
screen through which the sand drops while the pebbles slide down and
accumulate at the bottom. The cost of screening by hand is the cost of
shoveling the gravel against the screen divided by the number of cubic
yards of saved material. In screening gravel for sand the richer the
gravel is in fine material the cheaper will be the cost per cubic yard
for screening; on the contrary in screening gravel for the pebbles the
less sand there is in the gravel the cheaper will be the cost per cubic
yard for screening. The cost of shoveling divided by the number of
cubic
yards shoveled is the cost of screening only when both the sand and the
coarser material are saved. Tests made in the pit will enable the
contractor to estimate how many cubic yards of gravel must be shoveled
to get a cubic yard of sand or pebbles. An energetic man will shovel
about 25 cu. yds. of gravel against a screen per 10-hour day and keep
the screened material cleared away, providing no carrying is necessary.

A mechanical arrangement capable of handling a considerably
larger
yardage of material is shown by Fig. 8. Two men and a team are
required.
The team is attached to the scraper by means of the rope passing
through
the pulley at the top of the incline. The scraper is loaded in the
usual
manner, hauled up the incline until its wheels are stopped by blocks
and
then the team is backed up to slacken the rope and permit the scraper
to
tip and dump its load. The trip holding the scraper while dumping is
operated from the ground. The[Pg 22]
scraper load falls onto an inclined
screen which takes out the sand and delivers the pebbles into the
wagon.
By erecting bins to catch the sand and pebbles this same arrangement
could be made continuous in operation.

Fig. 8.—Device for Excavating and
Screening Gravel and
Loading Wagons.

In commercial gravel mining, the gravel is usually sorted into
several
sizes and generally it is washed as well as screened. Where the pebbles
run into larger sizes a crushing plant is also usually installed to
reduce the large stones. Works producing several hundred cubic yards of
screened and washed gravel per day require a plant of larger size and
greater cost than even a very large piece of concrete work will
warrant,
so that only general mention will be made here of such plants. The
commercial sizes of gravel are usually 2-in., 1-in., ½-in.
and ¼-in.,
down to sand. No very detailed costs of producing gravel by these
commercial plants are available. At the plant of the Lake Shore
&
Michigan Southern Ry., where gravel is screened and washed for ballast,
the gravel is passed over a 2-in., a ¾-in., a
¼-in. and a ⅛-in. screen
in turn and the fine sand is saved. About 2,000 tons are handled per
day; the washed gravel, 2-in. to ⅛-in. sizes, represents from 40 to 65
per cent. of the raw gravel and costs from 23 to 30 cts. per cu. yd.,
for excavation, screening and[Pg 23]
washing. The drawings of Fig. 9 show a
gravel washing plant having a capacity of 120 to 130 cu. yds. per hour,
operated by the Stewart-Peck Sand Co., of Kansas City, Mo. Where
washing
alone is necessary a plant of one or two washer units like those here
shown could be installed without excessive cost by a contractor at any
point where water is available. Each washer unit consists of two
hexagonal troughs 18 ins. in diameter and 18 ft. long. A shaft carrying
blades set spirally is rotated in each trough to agitate the gravel and
force it along; each trough also has a fall of 6 ins. toward its
receiving end. The two troughs are inclosed in a tank or box and above
and between them is a 5-in. pipe having[Pg 24]
¾-in. holes 3 ins. apart so
arranged that the streams are directed into the troughs. The water and
dirt pass off at the lower end of the troughs while the gravel is fed
by
the screws into a chute discharging into a bucket elevator, which in
turn feeds into a storage bin. The gravel to be washed runs from 2 ins.
to ⅛-in. in size; it is excavated by steam shovel and loaded into
1½
cu. yd. dump cars, three of which are hauled by a mule to the washers,
where the load is dumped into the troughs. The plant having a capacity
of 120 to 130 cu. yds. per hour cost $25,000, including pump and an
8-in. pipe line a mile long. A 100-hp. engine operates the plant, and
20
men are needed for all purposes. This plant produces washed gravel at a
profit for 40 cts. per cu. yd.

CONCRETE CONSTRUCTION METHODS AND COST

CHAPTER I.—METHODS AND COST OF SELECTING AND PREPARING
MATERIALS FOR CONCRETE.